In an optical communications system, information is encoded onto a light signal. The light signal is transmitted from one point to another, as for example by free-space light beams or optical fibers. At the receiving end, the information is read from the light signal.
An important advantage of optical communications is that a number of different light signals of different wavelengths may be mixed together (multiplexed) into a single light beam in a technique known as wavelength division multiplexing (WDM). Each light signal of a different wavelength, or channel, has information encoded onto it prior to the mixing of the channels. At the receiving end, the channels are separated, or demultiplexed, according to their wavelengths. The information on each channel is read from the demultiplexed light of that wavelength. A single multiplexed light beam may therefore carry many times the information that may be transmitted by a non-multiplexed light beam.
The multiplexing and/or demultiplexing may be accomplished using a series of light bandpass filters. Each filter is formed as a substrate and a multilayer dielectric light-transmissive optical stack deposited upon the substrate. The bandpass filter transmits only light of a specific wavelength. In the demultiplexing function, for example, when a multichannel beam is incident upon the filter, the light channel associated with the bandpass range is transmitted through the filter to a light receiver behind the filter. The beam with the remaining channels is reflected to another filter, where the next channel is extracted from the beam in a similar fashion, and so on until all of the channels of information carried by the light beam have been separated for further processing.
As the number of channels transmitted on a light beam increases, the number of multiplexing and/or demultiplexing bandpass filters increases. The multiplexing device structure becomes increasingly more complex and unwieldy, as well as subject to loss of alignment due to thermal effects and other reasons as the size of the structure increases. There is accordingly a need for an approach which accomplishes the multiplexing and/or demultiplexing function in a more convenient manner, particularly for large numbers of channels on the light beam. The present invention fulfills this need, and further provides related advantages.